1. Technical Field
The present invention relates to a semiconductor device and an electronic timepiece.
2. Related Art
Electronic timepieces such as wristwatches drive semiconductor devices in which electronic circuits are embedded using primary batteries or rechargeable secondary batteries as power supplies. To realize energy saving in electronic timepieces, there is known control reliably performed such that constant voltages ensuring normal operations of the semiconductor devices are generated by constant voltage generation circuits and power of the voltages is supplied to constant voltage driving circuits including oscillation circuits or CPUs (for example, see JP-A-2006-153669).
Incidentally, when a power supply voltage is reduced, a constant voltage generated by a constant voltage generation circuit is also reduced, becomes less than a minimum driving voltage of an oscillation circuit or a CPU, and thus an operation of the constant voltage driving circuit such as an oscillation circuit becomes unstable or is stopped. Thus, it is desirable to provide a constant voltage control circuit that stops the constant voltage generation circuit when the power supply voltage is reduced and that operates the constant voltage generation circuit when a power supply voltage is increased by exchanging a primary battery or recharging a secondary battery.
The constant voltage control circuit is driven with a power supply voltage. However, to realize further energy saving, the constant voltage control circuit is considered to be driven with a constant voltage generated by the constant voltage generation circuit.
However, when the constant voltage control circuit is driven with the constant voltage of the constant voltage generation circuit, the power supply voltage is reduced. Thus, when the constant voltage generation circuit is stopped and the constant voltage generation circuit does not operate, the constant voltage control circuit does not operate either. Therefore, a so-called deadlock state occurs, and thus a new problem may occur in that the constant voltage control circuit and the constant voltage generation circuit do not operate.